Code:
# cat file1
111,222,333,444,555,666
777,888,999,000,111,222
111,222,333,444,555,888
# cat file2
666,AAA
222,BBB
888,CCC
# sort -t, -k 6,6 -o file1 file1
# sort -t, -k 1,1 -o file2 file2
#cat file1 file2
777,888,999,000,111,222
111,222,333,444,555,666
111,222,333,444,555,888
222,BBB
666,AAA
888,CCC
# join -t, -o 1.1,1.2,1.3,1.4,1.5,1.6,2.2 -j1 6 -j2 1 file1 file2
777,888,999,000,111,222,BBB
111,222,333,444,555,666,AAA
111,222,333,444,555,888,CCC